Peak pair

The SECSY spectrum of buxapentalactone displays a number of off-diagonal peaks. Pairs of interconnected cross-peaks can be identified... 

For manual optimization methods the peak separation function, P, is easy to determine and can be calculated as shown in Figure 4.30 (479). The chromatographic response function for the chromatogram is then simply the sum of the In P values for the n adjacent peak pairs. 

Rather than the separation function, resolution between individual peak pairs is used in most automated optimization procedures because it is easier to calculate, although non-Gaussian pe2dcs and overlapping peaks can present problems due to the difficulty of estimating peak widths. A simple objective function would be to consider only the separation between the worst separated peak pair, ignoring all others. If a set of... 

Mom of the functions considered so far specifically tedce into account the nuitber of peaks found in the chroBatograa. If the object of the analysis is to detect the maximum nuaber of peaks, even if the resolution between individual peak pairs was poorer, then equations (4.47) and (4.48) would be inferior. A chroaatographic response function, CRF, that takes into account the siaultaneous iaportance of resolution, separation tiae, and the total nuaber of detectable pe2dcs can be e]q>ressed as follows... 

Figure 4.34 Peak-pair resolution naps and an overlapping resolution nap for the separation of nine substituted naphthalene compounds by reversed-phase liquid cbrosatography illustrated in Figure 4.33. (Reproduced with permission from ref. 545. Copyright Elsevier Scientific Publishing Co.)...

Nitrite can also be catalytically reduced by the Mb-CMC film electrode. When an Mb-CMC film electrode was placed in a pH 5.5 buffer containing N02, a new reduction peak appeared at about -0.8 V while the original Mb Fem/Fen peak pair at about -0.25 V was intact. This new peak increased with the concentration of N02 and the catalytic reduction peak of nitrite increased linearly with nitrite concentration in the range of 0.6-8mM with a detection limit of 0.32mM. Oxygen and hydrogen peroxide are also often detected by biosensors based on the direct electrochemistry of Mb in the Mb-CMC film electrode. 

From the data presented above, use adjacent peak pairs to calculate selectivity (a) and resolution (Rs). 

A tentative list of factors that may be investigated in the robustness test is presented in Table 8. This list is not complete and additional factors may be added. The limits for the factor levels are proposals and should be evaluated case by case. The significance of the effects of the factors on the responses such as the resolution of all peak pairs, the tailing factor, retention times, analysis time, etc., is evaluated. 

For example, to determine the empirical formula of di-n-octylphthalate, the daughter spectrum of the containing molecular ion (392) was obtained (Figure 7). The relative peak areas of adjacent peak pairs at m/z 149 and 150 is 2 1. This indicates that the M+1 ion is twice as likely to lose a atom as retain it. Thus the ratio of the number of carbon atoms lost to those retained is 2 1. Since the identified phthalate substructure contains 8 carbons, the unknown compound (di-n-octylphthalate) must contain 24 carbon atoms. These data, along with the molecular weight of 390 as determined from the conventional Cl mass spectrum of the unknown was fed into the empirical formula generator and the output was one empirical formula C24H38O4. 

The selectivity is demonstrated by analysis of a mixture of the relevant compounds, e.g., a selectivity batch/sample solution. The resulting electropherogram is compared with the selectivity electropherogram provided in the method description. The resolution between the critical peak pair(s) is determined. The target resolution should be >2.0 (the calculation... 

Parameters to measure in order to test robustness Resolution of critical peak pairs... 

For robustness testing, it is important to observe all relevant parameters, which include resolution of critical peak pairs and efficiencies. The means and additionally the standard deviations for all relevant peaks should be given for migration times (especially Jeof)) peak areas (PAs), and relative PAs (Table... 

In addition to that a quick system-suitability check should be done every day and when a system is restarted. The system-suitability test particularly emphasizes on resolution and sensitivity (single/concentration) or the DL. To save time, the system suitability test should restrict to repeatability of migration time and PA, and to resolution of relevant peak pairs. 

The overall separation potential of an electromigration technique can be expressed by the peak capacity ( ), which is defined as the maximum number of peaks that can be separated within a given separation time, usually coincident with the time interval between the first and last detected peak in the electropherogram, while retaining unit resolution for all adjacent peak pairs ... 

When we look at a separation to judge whether two peaks are separated, we look at the centers of the peaks, but more importantly, we look at the valley separating the peaks. An ideal separation is one in which all peak pairs are baseline separated the peak valleys all come down and touch the chromatographic baseline. If we were to draw a line connecting the two peak tops (Fig. 14.2, line 1-2), then drop a perpendicular line from the center of this connecting line to the baseline (A-B), the length of the resulting line would represent a standard of baseline separation for these two peaks. 

If the valley did not touch the baseline, it would have a length (A-C) that would be less than the distance to the baseline. If we divide the length of A-C by the length of A-B, we have a mathematical measure of the baseline resolution for the two peaks. Summing these ratios of baseline resolution for every peak pair gives us a resolution sum for the whole chromatogram. 

S-shaped current potential curves emerge when a surface phase transition of an organic adsorbate is coupled with a faradaic reaction of some electroactive species. As a representative of such a system, the periodate reduction on Au(lll) single crystal electrodes in the presence of camphor was studied [160], Camphor adsorbed on Au(lll) electrodes exhibits two first-order phase transitions upon variation of the electrode potential [161]. In a cyclic voltammogram, the phase transition manifests itself in a pair of needle-like peaks (Fig. 28 (A)). Between the peak pairs, a condensed, well-ordered camphor film exists. At more negative potentials, the camphor coverage is low, while the state of the adsorbate at positive potentials beyond the second phase transition is not yet known. The small hystereses between the respective anodic and cathodic peaks are caused by the finite nucleation rate of the respective thermodynamically stable phase. 

In this equation i represents the first eluting peak of a peak pair and j the last eluting peak. Hence, by definition a is always larger than unity. Sometimes a is called the separation factor, which is somewhat unfortunate terminology because separation is influenced by other factors than just a (see section 1.3). a is the chromatographic parameter that is most directly related to the selectivity of the phase system. In this book, therefore, the word selectivity will often be associated with a. Using eqns.(1.7) and (1.10) we can write two other equations for a, . 

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